Treatment of chromium ores



May 30, 1944- c. G. MAIER 2,349,801

TREATMENT OF CHROMIUM ORES Filed March 30', 1942 lNvEN-rorg (har/f5 (i.Maf/er ATTORNEY i Patented May 30, 1944 TREATMENT or CHROMIUM oREsCharles G. Maier, Oakland, Calif., assignor to The Dow Chemical Company,Midland, Mich., a corporation of 'Michigan Application March 30, 1942,Serial No. 430,774

(Cl. l-112) 16 Claims.

This application is a continuation in part of application Serial Number372,412 led'December 30, 1940.

This invention relates particularly to improved methods of chlorinationof oxidi'c ores carried out at elevated temperatures in whichcarbonaceous materials are used with chlorine to accomplish thechlorination. It is especially adapted to chlorination of chromite ore;the methods disclosed are of advantage in the treatment of all orescontaining alkaline earths such as magnesium in such an amount as topresent a sintering problem upon chlorination of the ore.

In practice, chromite ore is introduced into a suitable furnace, usuallya vertical column, along with a-carbonaceous reducing agent. Chlorine isusually introduced' into the furnace to pass counter-current to the ore.Temperatures suitable for the reduction and chlorination are maintainedin the furnace, the maximum usually being between 950 C. and 1050 C.although temperatures as high as 1250 C.can be employed. In

use, certain portions of the furnace are devoted to deinite operations;'and in the direction of ore passage through the furnace I have forconvenience designated these as the preheating zone wherein the OreV ispreheated, and the "chlorination zone wherein the actual reduction andchlorination occurs. Chlorine is usually introduced just below or beyondthe actual chlorination zone, usually at a point in the co1- umn which,in the direction of. ore passage, is beyond the point of maximumtemperature; in the case of chromite ore usually in a region at atemperature of about 850 to 950 C.

In the continuous reduction and chlorination of a chromite ore accordingto the method outlined, that is with carbon and chlorine in av verticalcolumn arranged for gravitational passage of ore, continuous operationwas occasionally hampered by formation of a solid,' ringlike flowrestricting accretion on the side wall of the column below thechlorination zone. These were found to be made up of ore and carbonbonded together largely by magnesium chloride. Such a ring was removedfrom the furnace only with d iflculty; frequentlyit could be removedonly by shutting down, cleaning'out the column and breakingl up 'therimnRing or accretion formation was more frequent and more aggravating whenthe rate of throughput of the rings are due to materials in theore,vsuch as lime and magnesia, that are converted by chlorination intothe Icorresponding 'chlorides which are fusible at the temperature ofthe chlorination. These molten chlorides upon solidifying may bond theore particles together into a mass capable of forming a bridge withinthe column or accretions upon the wall of the column. Such a mass iscemented or agglomerated by solidication of the molten chlorides. The-problem is particularly prevalent when low grade chromite ores high inmagnesia are employed; domestic ores are usually of this character. y

I have found that if, in that region in the furnace below thechlorination zone," which I will, for convenience, term the alkalineearth chloride solidiflcation zone or "solidilcation zone, I maintain anatmosphere whichA is free of chlorine and hydrogen chloride and is notadsorbed to any appreciable extent by the molten alkaline earthchlorides, these diiliculties are ore was high. ,One of the limitingfactors on the rateof throughput was the formation of these undesirable.solidifiedI masses on the wall defining the ore column. Apparentlythese accretions vor and hydrogen chloride.

overcome. The solidification zone extends from a point in the column, inthe direction of ore passage, which is at a temperature ihst below Aorat the melting point of magnesium chloride and calcium chloride andthrough the solidication range of these chlorides andianyother likemolten chlorides present. I have observed that the chlorides of calciumand magnesium do not wet silica in the presence of chlorine orhydroargon, or other gas non-adsorbable by the molten chlorides, whichatmosphere is free from chloride Thus the absence of chlorine andhydrogen chloride in the column through the critical solidicationtemperature range oi the alkaline earth chlorides results in.

hydrogen chloride free, non-adsorbable gas atmosphere, are thereforemaintained in the co1- umn immediately below the chlorination zone" andin that region wherein the molten alkaline earth chlorides solidify.Under this condition, the magnesium chloride, calcium chloride and otherlike chlorides. uniformly wet the remain,

' solidication and chlorination" zones.

ing .silicious material present (silica not being reduced or chlorinatedunder the furnace conditions) and are carried out on this instead ofcollecting and falling as liquid masses to solidify on the walls of thefurnace or on masses of residue region wherein the non-adsorbable gasatmosphere is maintained must be established in a proper spacedrelationship. That point in the furnace which is at the temperature offusion of the principal alkaline earth chloride provides a generallycritical upper limit in the furnace for the solidication zone. Thenon-adsorbable gas must be introduced into the furnace beyond or belowthat region which is at this temperature if it is to.be effective inenabling the chlorides towet uniformly the silicious material. Whenmagnesium chloride is the chief chloride to-which vattention must begiven, its fusion temperature, '708-711 C. is a critical 'upper limitfor location of thenon-adsorbable gas inlet. It is generally immaterialhow far below the fusion temperature point in the furnace thenon-adsorbable gas is introduced, the essential factor being a spatialseparation of the gas and chlorine inlets below and above the criticalpoint to ensure existence of denite and effective Introduction of thenon-adsorbable gas and its function will be further discussed.

The preferred process of this invention is one wherein a. considerableportion of the chlorine, if not all, is passed counter current to theore stream. Consequently at least some of the chlo-- rine is introducedat a point in the chlorination zone below the point of maximumtemperature. For reasons which will be presently explained, the inletfor this chlorine must -be provided at a point suiciently spaced fromthe solidification zone." If the chlorine inlet is too close to thesolidification'zone, the "chlorination zone will extend too far in thedirection of ore passage, possibly even into a region which is at atemperature where chromic chloride will condense in the ore stream.Additionally, the length of the non-ads'orbabl'e gas treating columnwill be undesirably reduced. If the chlorine inlet is too close to thepoint of maximum temperature in the chlorination zone, the length of,this will be shortened by the cooling action of the chlorine fed atordinary temperatures while the length of time that the ore is subjectedto chlorine will be unduly decreased.

I have found that the best point for introducv tion of chlorine in thechlorination zne is about half way between (a) the off-take from thefurnace for sublimed chlorides and (b) the point at which thetemperature in the' furnace corresponds to the fusion temperature of theprincipal alkaline earth chloride present. In the case of chromite oreswherein magnesium chloride is the principal molten chloride formed, thisis usually at a point which is at or about 900. C.; provided, however,that the point of entrance of chlorine whennsing the present v'inventionwith the auxiliary gas, should not be below-the normal condensationpoint of the vapors of chromium trichloride. This is near 850 C; formost chromite ores.

Chlorine is introduced in an amount suiliciently great to satisfy thestoichiometric requirements of the ore plus an excess adequate tomaintain about 10% free chlorine in the exit gases from the retort aftercondensation of sublimed chlorides for reasons pointed out at length inmy Patent 2,133,998 of October 25, 1938. At times not all of thechlorine need be added counter-currently below the chlorination zone.

The total requirements may be met by supplying from 50% to '15% of thechlorine countercurrently below the vapor exit, and the remainderconcurrently from above. This serves to increase the proportion ofcarbonyl or carbon chlorides which may be formed in the chloriadsorbablegas atmosphere to be maintained in the solidication zone" can beprovided by introducing carbon monoxide, nitrogen, helium, argon orother suitablevgas at the proper point in the furnace. Instead ofintroducing carbon monoxide as such it is possible to introduce oxygen,or an oxygen source as air, or a material decomposable in the column toyield oxygen, as a peroxide, a nitrate, chlorate or per-oxy compound, toreac't with carbon present in the hot residue in the furnace beyond thechlorination zone to form carbon monoxide. `When decomposable materialsare added, they are introduced at a point in the solidiflcation zonewhereas sufficient heat is present to ensure oxygen release and reactionto form carbon monoxide.

is present. Further, the use of .carbon monoxide has certain uniqueadvantages which will now be pointed out. It has been recognized bythose experienced in the chlorination of ores using carbonaceousmaterials with chlorine that considerable stoichiometric carbon excesses(usually 20%-30%) are required in order to secure high extraction of themetal values in the ores treated. Some carbon must therefore still bepresent when the last of the metal oxide particles in the ore are beingchlorinated. In a continuous counter-current unit, this corresponds tothe point of exit of the ore residue from the chlorination zone.Further, it has long been recognized that chlorinated carbonaceouscompounds, such as thechlorides of carbon, or carbon compoundsincompletely saturated with -oxygen such as carbon monoxide or carbonylchloride, produced an exceptionally smooth and readily controllablechlorination The value or cost of such materials is usually prohibitivefor commercial chlorination of ores. By using air to form carbonmonoxide, the advantages of using carbon chlorides can be securedwithout thei; high cost when they are produced and used as such.

The manner in which the process of my invention opera-tes with oxygenand excess carbon may be clarified by the following discussion: Oxygen,supplied in any convenient manner as by introducing air below thesolidiflcation zone,

contacts excess carbon in the spent ore in the 25% more than thestoichiometric requirements for allreductions and chlorinationsoccurring and producingcarbon"dioxide and chlorides. The

fication zonet' for reaction ,with they '.carb'on excess fi'ssuilicientstoichibmetricallyto react to form', carbon lfmonoxidi-:A with'only a.substantial portion,- from'f50,% :to185 of the carbon present in excessof that required bythe stoichiometry of the lreduction-chlori'natioxinreactions. f

When the carbon monoxide produced in that part of the column below lthechlorine inlet comes into contact with chlorine in the "chlorinationzone, carbonyl chloride and chlorides of carbon are formed, which atthese temperatures react rapidly with the oreinfa Vchlorinationreaction. The carbon monoxide ofthe "solidication zone gas stream isthus completely utilized.

It might be assumed thatthe introduction of some' air or oxygen with thechlorine fed directly to the "chlorination fzonef would first cause theformation of 'carbon monoxide, by interaction of carbon and oxygen, andthe carbon monoxide so formed could then'react partly -with chlorine toform carbonyl chloride, which in turn would act as a chlorinating agent,and thus permit the first chlorination. Such action is, however, verysilica, and I have-successfully usedthematerial known as Vitreosih,.At-the upper end foi fthe l shaft an,ore inletlfl provides forintroduction of V the ore charge nto ,casingfif` and thence into,

perature mairltaiil,ed..Y` t.

vparatus shown in the accompanying drawing in which Figure 1 is adiagrammatic view, partly in section, illustratingamapparatuswhich f,quantityfofioxygen'made available in theA solidisuccessfully employed.Figu 2.is a trating the retort-1 height.l ellativ In.this apparatusfja'l fprf vided. The shaft isfmade of inertmaterial yas the shaft furnaceproper.

Heating means, indicated at 8, kprovided inthe form of electricalresistances, is positioned about a. portion of the shaftintermediatethe'ends" thereof to provide the preheating zoneand thechlorination zone. `The upper portion of the shaft 6 is continued by acasing 32 to-'guide the ore charge into the column. The joint betweenthe shaft and extension is protected by a sure" rounding water coolingjacket 9. Some vchlorine Y is introduced through' an inlet Il placed atthe minor. Since itis desired to operate at temperatur'es YWhereat` thevchlorination of the ore is rapid, and with an excess of chlorine, theproduct of the chlorination reaction is always carbon dioxide: ratherthan carbon monoxide. Furthermore,'it is well known that theflrst'stepof the oxidation of carbon 'itself is invariably carbon dioxide'ratherthan carbon monoxide and *that f the latter material is obtainable as asecondary formation according to the so-called producer necessityforthe'correct spacial separation of .the r chlorine inlet and thenon-adsorbable gasinlet so that the proper'and lseparate chlorinationzone and solidiilcation zoneare' maintained.

1cm-ight .be further thought that the admission of air or oxygencontaining gases could promote the reactiono 1 andw thus maintain themagnesia in `the form of oxide. This has not -been found to be ,thecasev in practice. Obviouslyfthe conditions suited to this reaction aregenerally lll suited to the chlorination of ore. The` conclusion, fis,therefore.

that `when 4oxygen and chlorinetogether are simultaneouslyfpresent assuch inthe chlorination zone, magnesium cannot be `prevented from, chlo`rinatingnor ,can it be reoxidizedffrom the chloride formy to the oxide`form when'` active chloe rination -of ore occurs. y "l f vApparatus As aspecific and illustrative example of the manner in which my inventioncan be `carried out` successfully, the following operations aredisclosed, particularly inconjunctiony with the ap charge conveyors topof the shaft and the V'remainder' through fa' side inlet |5 providedtoward'the end of the chlorination zone."y A` movable thermocouple wellI4 extends downwardly into the shaft to enable tcmperatures to beascertained in the shaft.

Exit I6 for volatilized materials is placed above the lower end oftheheating zone. -At the base of the shaft another cooling-section Il isprovided, to protect the joint between shaft Gand a metal base structure33 and cool the materials' which pass therethrough to be removedl bydis- |8 in case I3 at the bottom of the shaft. 1 1

Volatilized products pass over through exit I5, into condenser"` 2lwhich is also madeof silica, usually Vitreosil. -Volatilized chloridescondensing on the side of the condenser 2l are removed by scraper 22onto plate 23. Another scraper 2l serves toV removecondensed chloridesalong plate 23 through passagei26,into areceiver 21. Dust, fines and thelike-are collected by filter bag 28 in housing 28. V:Rod "3L enables thebag 29 vto be l,

sh aken to remove collected materials. i 4(.)peratio'n The shaft furnace`wasbrought up totemperaf ture and filled with -a charge madeup bycoating. y massive carrier particles with a ,chromite `oreca-rbon mix.`The -ore-,used was ofthe `following composition:

. Percent-`v 'C1203 f.... l 48.15 FeO (total iron): i i 19.7 SlOz e5.3,4 MgO 16.5

CaO.4 ,3.8 Mn l f rtrace The chromite ore wasfirst lgrolindto 200 meshin a-dmixture with .20%,fif `gas, carbon." This`vl mixture wasthenplaced on carrier particles pre; pared and coated after themlannerldisclosedfin myPatent 2,133,997, d,

The carbony `quantity;'e'rr'iployed wa'sfLZ-S timesA the. quantityrequired stoichiometricallyto reduce all reducible oxides presentiAinintroduced through'the inletflifl into thefcolumn at apoint below the.sol idiflcationjzonef region. reacted with excess carbon present inthis regionto Aform carbon monoxideL` This was effe'ztiveas anon- The'highest temperature 4 adsorbable gas atmosphere in the solidication zoneduring the. entire The following results are taken from actual operatingrecords showing average conditions maintained during the sixth and theseventh day of continuous operation. They serve to illustrate howcontinuous operation was maintained in practice with the describedapparatus. The charging rate was 4 kilograms per hour of the coatedcarrier particles. The operation was very smooth and a high chromiumconversion was: effected.

Operation temperatures 'I'he temperatures in the retort vary over aconsiderable range and in Figure 2 I have indicated a rtypical thermalgradient through the retort. in the retort which is of significance, sofar as the sublimed ingredients. condensing in condenser 2l areconcerned, is that immediately adjacent the vapor off-take I6 for thisdetermines the composition of the mixed chlorides condensing. In case itis desired to have a large percentage of magnesium chloride and otheraccretion forming chlorides in the condensed mass, the temperature canbe maintained relatively high for magnesium chloride and the -otherchlorides are then more volatile. Temperatures of 1150 C. an'd upwardsto 1400 C. can be used.- I prefer, however, to maintain the condensateor sublimate-.in the receiver as free of magnesium chloride as ispossible and therefore operate at a temperature of about 900 C. andusually between 900 C. and 1100 C.

The purging operation In the above tabulation of operations mention ismade of fMg discharged as magnesium chloride in purge. This following isin explanation ofthis: l

When the retort material is of silica-the dispersing action of theinert, chlorine free gas causes the walls of the retort to also be wetin a manner similar to the silicious carrier particles or ore residue.After extended operating periods, this may cause the slow formation of aring near the upper end of the Solidincation zone, al through'much lesssoon than if no non-adsorbable gas atmosphere is employed. This smallquantity of magnesium chloride dispersed on the Days of operation 6th'1th Temperature of vapor exit I6 in C 1,010 1,045 Ore rate, gms/hr 264308 Chlorine input Aconcurrent from top, liters/hr. (inlet II) 82 89Chlorine input counter-current frombelow, liters/hr. (inlet I5) 101 109Air input, liters/hr. (inlet I2) 43 46 Ore burden, gms/kg. carrier 66'I7 Extraction per cent of contained CrzOa 99.4 98.9 Per cent of totalMgO retained as nitido 2.3 2.2 Per cent of total Mg discharged asmagnesium chloride on carrier- 48.7 74:3 Per cent of total Mg dischargedas magnesium chloride in purge 1.5 3.1 Per cent of total Mg volatilizeda as chloride 47 20.4

from an upper portion of said zone to leave a walls is advantageouslyremoved by periodic purging charges of inert particles containing anamount of carbon equivalent to the normal excess, but carrying no ore.This purge, which may normally require about one-half hour per day ofoperation, results in a slightly altered temperature gradient, and inthe renewed distribution of the alkaline earth chloride from the'wallsto lthe inert particles.

other O'leS WhileI have described my invention with particular referenceto chromite ores, it is, of course, to be understood that it isapplicable to other chromium containing materials particularly thosecontaining magnesium, calcium or other alkaline earth metal oxides orother materials wherein the formation of molten chlorides such asmagnesium chloride presents an accretion or ring formation problem. Inaddition, the use of carrier particles. although advantageous in manyways, need not be rigidly adhered to and the charge can be an ore-carboncharge or an ore charge in any suitable form with the carbon suitablysupplied.

I claim:

l. In a continuous countercurrent process for chlorination in a verticalcolumn of a chromite ore containing silica and magnesia, the steps ofmaintaining a chlorination zone in an upper portion of said columnwherein said ore is reduced and chlorinated and volatilized chloridesare formed, removing said chlorides from an upp'er portion of said zoneto leave a mass of spent ore in said column in another zone below saidchlorination zone, maintaining said other zone at a temperature whereatmagnesium chloride present solidiiies, and maintaining in said otherzone a gaseous atmosphere substantially non-adsorbable by said magnesiumchloride and which is free of chlorine and hydrogen chloride wherebysaid magnesium chloride wets the silica present and is carried out ofsaid other zone on the silica.

2. In a continuous countercurrent process for chlorination in a verticalcolumn of a iinely divided chromite ore containing silica and materialsnormally causing agglomeration of the ore, the steps of maintaining achlorination zone in anI upper portion of said column wherein said oreis reduced and chlorinated and volatilized chlorides are formed,removing said chlorides mass of spent ore in said column in another zonebelow said chlorination zone, maintaining said other zone at atemperature whereat chlorinated materials normallyA causing sinteringsolidify, and maintaining in said other zone a gaseous atmospheresubstantially non-adsorbable by said chlorinated materials and which isfree of chlorine and hydrogen chloride whereby said chlorinatedmaterials wet the silica present and are carried outof said other zoneon the silica.

3. In a continuous countercurrent process for chlorination of chromiteores containing silica and magnesio. wherein the ore is reduced with acarbonaceous material and chlorinated in a column, the steps ofadmitting oxygen into the .column at a point whereat below about 711process for steps consisting of introducing an ore-carbon.

chlorination of chromite ores containing silica and magnesia wherein theore is reduced with a carbonaceous material and chlorinated in a column,the'step of maintaining a vsubstantially chlorine and hydrogenchloridefree gaseous atmospherenon-adsorbable by magnesium chloride in thatportion of the column wherein magnesium chloride solidies whereby liquidmagnesium chloride wets the silica.

5. In a continuous countercurrent process for thechlorination of orescontaining silica and magnesia wherein the-ore is reduced with acarbonaceous material and chlorinated in a column, Ythe stepsv ofadmitting air to react with carbon v-and form a carbon monoxideatmosphere in that portion of the ore column which is at a temperaturebelow the melting point and in the solidiiication range of magnesiumchloride whereby liquid magnesium chloride wets the silica, and,admitting chlorine into that portion of the column which is above themelting point of magnesium chloride.

6. In a continuous chlorination-process for an oxidic ore wherein theore is reduced in the presence of silica in a furnace heated to anelevated temperature with carbon present in admixture with the ore, theore containing alkaline earth components which are chlorinatable to formliquid alkaline earth chlorides causing cementing of ore particles uponsolidication of said liquid chlorides, the steps comprising moving astream of said ore and carbon through said furnace, introducing anoxygen containing gas into said stream to react with said carbon andform carbon monoxide in the substantial absence of chlorine whereby anyalkaline earth chlorides wet the silica, and introducing chlorine intosaid ore stream at a point whereat carbon monoxide formation issubstantially complete.

7. In a continuous countercurrent process for -chlorination of chromiteores containing magnesia wherein the ore is reduced in the presence ofsilica with a carbonaceous material and chlorinated in a heated column,the steps of admitting an oxygen containing gas into the column at apoint whereat the temperature is below about 711 C. and whereat theoxygen 'containing gas reacts to form carbon monoxide with carbonaceousmaterial present, in the substantial absence of chlorine whereby anyalkaline earth chlorides wet the silica and are carried out of thecolumn on the silica and admitting chlorine at a point in the. columnwhereat the temperature is above about 850 C. and carbon monoxideformation is substantially complete.

8. In a ohromite ore chlorination process, the steps consisting ofyintroducing an ore-carbon vstream also `containing silica into thetop ofa vertical shaft furnace, the carbon being present in excess of thatquantity required stoichiometrically to reduce the reducibleconstituents present in the ore, maintaining temperatures in saidfurnace promoting reduction and chlorination of said ore, introducingchlorine at a point in said furnace which is below the region of maximumtemperature and which is at a temperature of about 900 C., andintroducing an oxygen containing gas to react substantially completelywith carbon present in said stream in that region in said furnace whichis below said point of chlorine introduction and below a temperaturewhereat any alkaline earth chlorides condense whereby said chlorides wetthe silica present and are carried out on the silica.

9. In a chromite ore chlorination process, the

stream also containingv silica into the top of a vertical shaft furnace,the carbon being present in excess of that quantity requiredstoichiometrically to reduce the reducible constituents present in theore, `maintaining temperatures inrsaid furnace promoting reduction andchlorination of said ore,l introducing chlorine at a point in saidfurnace which is below the region of maximum temperature and which is ata temperature of about 900 C., and introducing air to reactsubstantially completely with carbon present in said stream in thatregion in Said furnace which is below said point of chlorineintroduction and below a temperature of about 711 C. whereby anyalkaline earth chlorides present condense and wet the silica present andare carried out on the silica.

10. In a continuous countercurrent ore chlorination process conducted ina shaft furnace and utilizing an ore-carbon mixture dispersed onrelatively massive carrier particles, and separately introduced air andchlorine, the step of periodically purging said furnace with carrierparticles substantially free of ore, while maintaining llow of air,chlorine and carbon.

11. 'I'he process of claim 4. wherein the gaseous atmosphere issubstantially carbon monoxide.

12. The process of claim 4 wherein the gaseous atmosphere is composedlargely of nitrogen.

13. In a continuous countercurrent process for chlorination in avertical column of a chromium containing material including magnesiumand silica, the steps of maintaining a chlorination zone in an upperportion ofsaid column wherein said ore is reduced and chlorinated,maintaining said chlorination zone at a temperature sufficiently high tovolatilize at least partially metal chlorides formed in said zone andwhich chlorides pass off as volatilized chlorides from an upper portionof said column to leave a spent ore mass in said column in another zonebelow said chlorination zone, maintaining said other zone at atemperature whereat magnesium chloride solidifies, and maintaining achlorine and hydrogen chloride free atmosphere in said other zone whichis substantially non-absorbable by said magnesium chloride whereby themagnesium chloride is carried out on the silica.

14. In a continuous countercurrent process for chlorination in avertical column of a chromium containing material including magnesiumand silica, the'hsteps of maintaining a chlorination zone in an upperportion of said column wherein said ore is reduced and chlorinated,maintaining said chlorination zone at a temperature betweenV about 850 Cand 1400 C. to volatilize at least partially metal chlorides formed insaid zone and which'chlorides pass ofi as volatilized chlorides from anupper portion of said column to leave a spent ore mass in said column inanother zone below said chlorination zone, maintaining said other zoneat a temperature below about 711 C. and whereat magnesium chloridesolidies, and maintaining a chlorine and hydrogen chloride freeatmosphere in said other zone which is substantially non-absorbable bysaid magnesium chloride whereby the magnesium chloride wets the silicapresent and is carried out of the column on the silica.

15. In a continuous countercurrent process for chlorination in avertical column of a chromium containing material including magnesiumand silica, the stepsof maintaining a chlorination zone in an 4upperportion of said column wherein 6 said o're is reduced and chlorinated,ummming said chlorination zone at a temperature beabout 711 C., andmaintaining a chlorine and hydrogen chloride free'atmosphere in saidother zone which is substantially non-absorbable by said magnesiumchloride whereby the magnesium chloride wets the silica present and iscarried out of the column on the silica.

16. In a process for chlorination in a vertical column of a chromiumcontaining material including silica and atleast one alkaline earthcomponent, the steps of maintaining a reductionchlorination zone in saidcolumn wherein reduction and chlorination of chromium and said componentoccurs at a temperature between about 850 C. and 1400" C., andmaintaining, in another zone in said column below said chlorinationzone, a temperature below about 711 C. and a chlorine and hydrogenchloride free atmosphere substantially non-absorbable by a chloride o!said component whereby said component wets the silica present.

CHARLES G. MAIER.

